Compressionion of pulse code modulation signal using type IV discrete cosine transform based on the mp3 model
Chepyegon, Andrew Yotui
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Digital signal compression in the recent past has become the mainstay of the basic technologies of multimedia due to the bandwidth and storage limitations inherent in networks and computers. The change from circuit switched to packet switched systems in the telecommunication infrastructure in the past few years, has reflected on the way Pulse Code Modulation (PCM) signal which in essence is a raw audio signal, is carried in present systems. The purpose of this study was to design an application that utilizes type IV Discrete Cosine Transform (DCT IV), also known as the Modified Discrete Cosine Transform (MDCT) techniques to compress Sound of compact disk (CD) quality digital audio that has been encoded using the Motion Picture Experts Group (MPEG)-1 Audio Layer III (MP3) standard. Visual Basic.NET programming language has been used to achieve this. Although the compression technique used in this research project was a lossy one, the perceptual analysis showed no significant deviation between the raw uncompressed pulse code modulation (PCM) samples and the filtered MDCT output which uses psychoacoustic principles and MPEG psychoacoustic signal analysis to describe the hybrid filter bank design issues and algorithms. The results obtained from capturing raw audio signal at a bit rate of 128 kbps through three sampling rates namely 32 KHz, 41 KHz and 48 KHz were reviewed. The results showed a major improvement on the compression rate as a result of the MDCT application based on the MP3 compression standard. A significant data reduction of upto 90 percent of the original audio file was achieved when the MDCT coding was applied to raw uncompressed audio files based on the widely used MPEG-1 Audio Layer III (MP3) compression standard. In testing the quality of the compressed audio, subjective tests and the performance of Perceptual Evaluation of Audio Quality (PEAQ) software for objective audio quality measures for the prediction of the perceived quality of compressed files were investigated, and both the objective and subjective analysis showed high correlations.